5,523 research outputs found
Relevant results from the NA48 experiment
We report relevant results from NA48 experiment at CERN SPS. NA48 was
proposed in 1990 \cite{proposal} to study direct CP violation in
to a level of accuracy sufficient to resolve the inconclusive status left by
the previous measurements performed by NA31 \cite{NA31} and E731 \cite{E731}.
In 2002 NA48 published the final result \cite{NA48epsoeps}. Small modification
to the experimental setup have allowed NA48 to go forward with an extensive
investigation of rare decays and hyperon decays. Some results are already
available and reported here together with the final CP violation measurement.Comment: 3 pages, 1 eps figure, XXIII Physics in collisio
Signatures of rocky planet engulfment in HAT-P-4. Implications for chemical tagging studies
Aims. To explore the possible chemical signature of planet formation in the
binary system HAT-P-4, by studying abundance vs condensation temperature Tc
trends. The star HAT-P-4 hosts a planet detected by transits while its stellar
companion does not have any detected planet. We also study the Lithium content,
which could shed light on the problem of Li depletion in exoplanet host stars.
Conclusions. The exoplanet host star HAT-P-4 is found to be ~0.1 dex more metal
rich than its companion, which is one of the highest differences in metallicity
observed in similar systems. This could have important implications for
chemical tagging studies, disentangling groups of stars with a common origin.
We rule out a possible peculiar composition for each star as lambda Boo, delta
Scuti or a Blue Straggler. The star HAT-P-4 is enhanced in refractory elements
relative to volatile when compared to its stellar companion. Notably, the
Lithium abundance in HAT-P-4 is greater than in its companion by ~0.3 dex,
which is contrary to the model that explains the Lithium depletion by the
presence of planets. We propose a scenario where, at the time of planet
formation, the star HAT-P-4 locked the inner refractory material in
planetesimals and rocky planets, and formed the outer gas giant planet at a
greater distance. The refractories were then accreted onto the star, possibly
due to the migration of the giant planet. This explains the higher metallicity,
the higher Lithium content, and the negative Tc trend detected. A similar
scenario was recently proposed for the solar twin star HIP 68468, which is in
some aspects similar to HAT-P-4. We estimate a mass of at least Mrock ~ 10
Mearth locked in refractory material in order to reproduce the observed Tc
trends and metallicity.Comment: 5 pages, 6 figures, A&A Letters accepte
The XMM/BeppoSAX observation of Mkn 841
Mkn 841 has been observed simultaneously by XMM and BeppoSAX in January 2001.
Due to operational contingency, the 30ks XMM observation was split into two
parts, separated by about 15 hours. We first report the presence of a narrow
iron line which appears to be rapidly variable between the two pointings,
requiring a non-standard interpretation. We then focus on the analysis of the
broad band (0.3-200 keV) continuum using the XMM/EPIC, RGS and SAX/PDS data.
The Mkn 841 spectrum is well fitted by a comptonization model in a geometry
more photon-fed than a simple slab geometry above a passive disk. It presents a
relatively large reflection (R>2) which does not agree with an apparently weak
iron line. It also show the presence of a strong soft excess wellfitted by a
comptonized spectrum in a cool plasma, suggesting the presence of a
multi-temperature corona.Comment: 4 pages, 5 figures. Proc. of the meeting: "The Restless High-Energy
Universe" (Amsterdam, The Netherlands), E.P.J. van den Heuvel, J.J.M. in 't
Zand, and R.A.M.J. Wijers Ed
Multiwavelength campaign on Mrk 509. V. Chandra-LETGS observation of the ionized absorber
We present here the results of a 180 ks Chandra-LETGS observation as part of
a large multi-wavelength campaign on Mrk 509. We study the warm absorber in Mrk
509 and use the data from a simultaneous HST-COS observation in order to assess
whether the gas responsible for the UV and X-ray absorption are the same. We
analyzed the LETGS X-ray spectrum of Mrk 509 using the SPEX fitting package. We
detect several absorption features originating in the ionized absorber of the
source, along with resolved emission lines and radiative recombination
continua. The absorption features belong to ions with, at least, three distinct
ionization degrees. The lowest ionized component is slightly redshifted (v =
+73 km/s) and is not in pressure equilibrium with the others, and therefore it
is not likely part of the outflow, possibly belonging to the interstellar
medium of the host galaxy. The other components are outflowing at velocities of
-196 and -455 km/s, respectively. The source was observed simultaneously with
HST-COS, finding 13 UV kinematic components. At least three of them can be
kinematically associated with the observed X-ray components. Based on the
HST-COS results and a previous FUSE observation, we find evidence that the UV
absorbing gas might be co-located with the X-ray absorbing gas and belong to
the same structure.Comment: 12 pages, 7 figures, 9 tables. Accepted for publication in Astronomy
& Astrophysic
High resolution X-ray spectroscopy of the Seyfert 1 Mrk841: insights into the warm absorber and warm emitter
The Seyfert 1 galaxy Mrk841 was observed five times between 2001 and 2005 by
the XMM-Newton X-ray observatory. The source is well known for showing spectral
complexity in the variable iron line and in the soft X-ray excess. This paper
reports on the first study of Mrk841 soft X-ray spectrum at high spectral
resolution. The availability of multiple exposures obtained by the Reflection
Grating Spectrometer (RGS) cameras allows a thorough study of the complex
absorption and emission spectral features in the soft X-ray band.The three
combined exposures obtained in January 2001 and the two obtained in January and
July 2005 were analysed using the SPEX software. We detect a two-phase warm
absorber: a medium ionisation component (logxi~1.5-2.2 ergs s cm^{-1}) is
responsible for a deep absorption feature in the Unresolved Transition Array of
the Fe M-shell and for several absorption lines in the OVI-VIII band; a higher
ionisation phase with logxi~3 ergs s cm^{-1} is required to fit absorption in
the NeIX-X band. The ionisation state and the column density of the gas present
moderate variation from 2001 to 2005 for both phases. The high ionisation
component of the warm absorber has no effect in the Fe K band. No significant
velocity shift of the absorption lines is measured in the RGS data. Remarkably,
the 2005 spectra show emission features consistent with photoionisation in a
high density (n_e>10^{11} cm^{-3}) gas: a prominent OVII line triplet is
clearly observed in January 2005 and narrow Radiative Recombination Continua
(RRC) of OVII and CVI are observed in both 2005 data sets. A broad Gaussian
line around 21.7 Angstrom is also required to fit all the data sets. The
derived radial distance for the emission lines seems to suggest that the
photoionisation takes place within the optical Broad Line Region of the source.Comment: In press on A&A, replaced version includes language editing and typo
on velocities corrected in Table
A Long Observation of NGC 5548 by BeppoSAX: the High Energy Cut-off, Intrinsic Spectral Variability and a Truly Warm Absorber
NGC 5548 was observed by BeppoSAX in a single long (8 day) observation from
0.2 to 200 keV. We find (1) the spectral variation of the source is produced by
a change of the intrinsic power law slope; (2) a high energy cut-off at keV with a hint of change of with flux; (3) OVII and
OVIII absorption K edges, and a possible blended OVII-OVIII K
emission feature at keV, inconsistent with a purely
photoionized gas in equilibrium. We propose that the temperature of the
absorbing and emitting gas is K so that both collisional ionization
and photoionization contribute.Comment: 23 pages, 8 figures. Accepted for publication in The Astrophysical
Journa
Anatomy of the AGN in NGC 5548: V. A clear view of the X-ray narrow emission lines
Context. Our consortium performed an extensive multi-wavelength campaign of
the nearby Seyfert 1 galaxy NGC 5548 in 2013-14. The source appeared unusually
heavily absorbed in the soft X-rays, and signatures of outflowing absorption
were also present in the UV. He-like triplets of neon, oxygen and nitrogen, and
radiative recombination continuum (RRC) features were found to dominate the
soft X-ray spectrum due to the low continuum flux.
Aims. Here we focus on characterising these narrow emission features using
data obtained from the XMM-Newton RGS (770 ks stacked spectrum).
Methods. We use SPEX for our initial analysis of these features.
Self-consistent photoionisation models from Cloudy are then compared with the
data to characterise the physical conditions of the emitting region.
Results. Outflow velocity discrepancies within the O VII triplet lines can be
explained if the X-ray narrow-line region (NLR) in NGC 5548 is absorbed by at
least one of the six warm absorber components found by previous analyses. The
RRCs allow us to directly calculate a temperature of the emitting gas of a few
eV ( K), favouring photoionised conditions. We fit the data with a
Cloudy model of log erg cm s, log cm and log v km s for the emitting
gas; this is the first time the X-ray NLR gas in this source has been modelled
so comprehensively. This allows us to estimate the distance from the central
source to the illuminated face of the emitting clouds as pc,
consistent with previous work.Comment: Accepted by A&A, 15 pages, 6 figure
Multiwavelength campaign on Mrk 509. XIII. Testing ionized-reflection models on Mrk 509
Active Galactic Nuclei (AGN) are the most luminous persistent objects in the
universe. An excess of X-ray emission below about 2 keV, called soft-excess, is
very common in Type 1 AGN spectra. The origin of this feature remains debated.
Originally modeled with a blackbody, there are now several possibilities to
model the soft-excess, including warm Comptonization and blurred ionized
reflection. In this paper, we test ionized-reflection models on Mrk 509, a
bright Seyfert 1 galaxy for which we have a unique data set, in order to
determine whether it can be responsible for the strong soft-excess. We use ten
simultaneous XMM-Newton and INTEGRAL observations performed every four days. We
present here the results of the spectral analysis, the evolution of the
parameters and the variability properties of the X-ray emission. The
application of blurred ionized-reflection models leads to a very strong
reflection and an extreme geometry, but fails to reproduce the broad-band
spectrum of Mrk 509. Two different scenarios for blurred ionized reflection are
discussed: stable geometry and lamp-post configuration. In both cases we find
that the model parameters do not follow the expected relations, indicating that
the model is fine-tuned to fit the data without physical justification. A
large, slow variation of the soft-excess without counterpart in the hard X-rays
could be explained by a change in ionization of the reflector. However, such a
change does not naturally follow from the assumed geometrical configuration.
Warm Comptonization remains the most probable origin of the soft-excess in this
object. Nevertheless, it is possible that both ionized reflection and warm
Comptonization mechanisms can explain the soft-excess in all objects, one
dominating the other one, depending on the physical conditions of the disk and
the corona.Comment: 12 pages, A&A accepte
An enshrouded AGN in the merging starburst system Arp~299 revealed by BeppoSAX
Using a long (=150 ksec), broad-band (0.1--40 keV) BeppoSAX observation of
the merging starburst system Arp 299 (=IC 694 + NGC 3690) we found the first
unambiguous evidence of the presence of a deeply buried (N_H = 2.5E24 cm-2) AGN
having an intrinsic luminosity of L(0.5-100 keV) = 1.9E43 cgs. The X-ray
spectral properties of this AGN are discussed in detail as well as the thermal
component detected at soft X-ray energies which, most likely, is associated
with the starburst.Comment: 4 pages, 2 figures, Latex manuscript, Accepted for publication in
Astrophysical Journal - Letters Editio
Multiwavelength campaign on Mrk 509 XII. Broad band spectral analysis
(Abridged) The simultaneous UV to X-rays/gamma rays data obtained during the
multi-wavelength XMM/INTEGRAL campaign on the Seyfert 1 Mrk 509 are used in
this paper and tested against physically motivated broad band models. Each
observation has been fitted with a realistic thermal comptonisation model for
the continuum emission. Prompted by the correlation between the UV and soft
X-ray flux, we use a thermal comptonisation component for the soft X-ray
excess. The UV to X-rays/gamma-rays emission of Mrk 509 can be well fitted by
these components. The presence of a relatively hard high-energy spectrum points
to the existence of a hot (kT~100 keV), optically-thin (tau~0.5) corona
producing the primary continuum. On the contrary, the soft X-ray component
requires a warm (kT~1 keV), optically-thick (tau~15) plasma. Estimates of the
amplification ratio for this warm plasma support a configuration close to the
"theoretical" configuration of a slab corona above a passive disk. An
interesting consequence is the weak luminosity-dependence of its emission, a
possible explanation of the roughly constant spectral shape of the soft X-ray
excess seen in AGNs. The temperature (~ 3 eV) and flux of the soft-photon field
entering and cooling the warm plasma suggests that it covers the accretion disk
down to a transition radius of 10-20 . This plasma could be the
warm upper layer of the accretion disk. On the contrary the hot corona has a
more photon-starved geometry. The high temperature ( 100 eV) of the
soft-photon field entering and cooling it favors a localization of the hot
corona in the inner flow. This soft-photon field could be part of the
comptonised emission produced by the warm plasma. In this framework, the change
in the geometry (i.e. ) could explain most of the observed flux and
spectral variability.Comment: 19 pages, 14 figures. Accepted for publication in A&
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